A watch case having the characteristics which have just been listed is known from the Swiss Pat. No. 643,425 corresponding to U.S. Pat. No. 4,490,052. It comprises in particular a caseband on the upper surface of which is fastened a planar crystal by means of fixation means forming slots in which the edges of the crystal are held after having been laterally engaged therein and a seal placed against the periphery of the lower surface of the crystal. The slots in the fixation means are defined by two surfaces facing one another between which the crystal is engaged, the upper surface of the slots bearing against the upper surface of the crystal. The case includes moreover means for urging the seal against the lower surface of the crystal only after engagement of the crystal in the slots.
It is evident that the invention described in the cited patent is confined to watch cases equipped with a planar crystal and that it gives no teaching which would enable the application thereof to a crystal having the form of a spherical cap.
A crystal having this latter form is interesting since on the one hand it gives the impression that the watch is very thin, on the condition that said crystal is mounted having its edges matching the edges of the caseband at least on a major portion of the periphery, and on the other hand it exhibits better shock resistance than when a planar crystal is employed.